Hi Michael,
From your description, it really doesn't sound like the timing chain, although the timing chain is about the only weak link (no pun intended) that particular engine has. I have another question for you. Has the engine ever been overheated? You are describing the kind of noise that piston slap makes - the piston is a little sloppy in the cylinder bore, but after it warms up the skirt expands enough to take up the slack and the noise goes away. This kind of problem can be brought on by overheating, even for a very short period of time. How many miles does the engine actually have? If it's around 100k, you should definetly have the timing chain serviced, regardless of it's apparent condition. Have you changed the brand of oil recently, or gone to a synthetic lube? Get back to the board if you can supply these answers!